Mechanical properties of waterproofed gypsum boards with polydimethylsiloxanes

Abstract

A waterproofed gypsum board and associated method are provided, featuring the use of a mixture of magnesium oxide and a gypsum crystal modifier for improving the resistance to sagging of the waterproofed gypsum board, in particular, in moist and warm climatic conditions.

The invention claimed is: 
     
         1 . A waterproofed gypsum board, comprising: the gypsum board is waterproofed by means of at least one polysiloxane and includes magnesium oxide as a catalyst for the polymerisation of the at least one polysiloxane; the gypsum board being formed from a gypsum slurry which includes a calcium sulfate and a gypsum crystal modifier; wherein the gypsum crystal modifier is effective during the production of the gypsum board in the rehydration from hemihydrate to dihydrate; wherein the crystal modifier enhances the sag resistance of the gypsum board; wherein the gypsum crystal modifier includes at least one bivalent heavy metal salt which is selected from a group consisting of chlorides, hydroxides, oxides or combinations thereof; and wherein the content of the gypsum crystal modifier is between 0.01 and 0.3% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry. 
     
     
         2 . The waterproofed gypsum board according to  claim 1 , characterised in that the polysiloxane comprises a polydimethylsiloxane. 
     
     
         3 . The waterproofed gypsum board according to  claim 1 , characterised in that the at least one bivalent heavy metal salt is selected from a group consisting of copper salts, zinc salts, iron salts, tin salts and mixtures thereof. 
     
     
         4 . The waterproofed gypsum board according to  claim 1 , characterised in that the gypsum crystal modifier further comprises at least one borate which is selected from Me 2 B 4 O 7 , MeB 5 O 8 , Me 2 B 10 O 16 , and Me 2 B 8 O 13 , or mixtures thereof, with Me=alkali metal. 
     
     
         5 . The waterproofed gypsum board according to  claim 1 , characterised in that the content of magnesium oxide is between 0.01 and 1% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry. 
     
     
         6 . The waterproofed gypsum board according to  claim 1 , characterised in that the at least one bivalent heavy metal salt is selected from a group consisting of hydroxides, oxides, or combinations thereof. 
     
     
         7 . A method for producing the waterproofed gypsum board of  claim 1 , comprising the following steps:
 a) producing a slurry by mixing one or more calcium sulfate phases capable of setting,
 water, 
 the at least one polysiloxane, 
 magnesium oxide and 
 a gypsum crystal modifier, wherein the crystal modifier enhances the sag resistance of the gypsum board; and 
   b) shaping the mixture.   
     
     
         8 . The method according to  claim 7 , characterised in that the slurry additionally contains additives, including at least one of surfactants, foam formers, setting accelerators, setting retarders, starches, starch ethers, plasticisers, or means for improving the water retention. 
     
     
         9 . A waterproofed gypsum board, comprising: the gypsum board is waterproofed by means of at least one polysiloxane and includes magnesium oxide as a catalyst for the polymerisation of the at least one polysiloxane; the gypsum board being formed from a gypsum slurry including a calcium sulfate and a gypsum crystal modifier; wherein the gypsum crystal modifier is effective during the production of the gypsum board in the rehydration from hemihydrate to dihydrate; wherein the crystal modifier enhances the sag resistance of the gypsum board; wherein the gypsum crystal modifier includes at least one metal silicate; wherein the at least one metal silicate is a potassium silicate and belongs to the class of condensed silicates; and wherein the content of the gypsum crystal modifier is 0.3% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry. 
     
     
         10 . The waterproofed gypsum board according to  claim 9 , characterised in that the polysiloxane comprises a polydimethylsiloxane. 
     
     
         11 . The waterproofed gypsum board according to  claim 9 , characterised in that the content of magnesium oxide is between 0.01 and 1% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry. 
     
     
         12 . The waterproofed gypsum board according to  claim 9 , characterised in that the gypsum crystal modifier further comprises at least one borate which is selected from Me 2 B 4 O 7 , MeB 5 O 8 , Me 2 B 10 O 16 , Me 2 B 8 O 13 , and mixtures thereof with Me=alkali metal. 
     
     
         13 . A waterproofed gypsum board, comprising: the gypsum board is waterproofed by means of at least one polysiloxane and includes magnesium oxide as a catalyst for the polymerisation of the at least one polysiloxane; the gypsum board being formed from a gypsum slurry which includes a calcium sulfate and a gypsum crystal modifier; wherein the gypsum crystal modifier is effective during the production of the gypsum board in the rehydration from hemihydrate to dihydrate; wherein the crystal modifier enhances the sag resistance of the gypsum board; wherein the gypsum crystal modifier includes copper sulfate pentahydrate; wherein the content of the polysiloxane is 0.28% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry; wherein the content of the magnesium oxide is 0.15% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry; wherein the content of the copper sulfate is 0.05% by weight, in relation to the mass of the calcium sulfate in the gypsum slurry.